To jam and learn the simple chords for Ghost - Mary On A Cross chords, practice playing B, F#, G#m, B, D#, G#m, E, B, G#m and F# in sequence. Start with a comfortable 64 BPM and as you become proficient, aim for the song's BPM of 129. Considering the song's key of B Major, position your capo to suit your vocal and chord preferences.